DLC - Actual gameplay...

Were you talking about something like... Depression Quest? *duck and cover*

Specially the one with game ending.
Like Ubisoft did with Prince of Persia 2008.

I had no specific game in mind, but it's a trend things COULD go if the soundtrack had to be bought separately to enjoy while playing.

Other things they could make DLC...

Subtitles, mouse cursor/controls, all additional playable classes locked behind DLC.

Suddenly i'm reminded of a flash game i played, which was something like progression quest or something, which started off in the game you had to take a loan of like $50 to get the start menu to work, then it was a simple vertical shooter where the money you earned in game upgraded the game a little at a time until finally it looked like a decent game. It got away with it because it was a free little fun game. If it were for real...

Poor guy, he's just too used to games on Steam :P

That was actually going to be my reply when I read the OP. :P
I think that one already exists: http://store.steampowered.com/app/230050/

I just thought of DQ because it has no actual gameplay - not even as DLC.

Actually thinking about it, the OP's question is not so silly. I can see ie. GTA-likes having DLC with extra radio stations, and I can see see people buying stuff like that, esp. if they include "exclusive" and popular artists.